Percent of Power with FP Prop

[lrfrey]

I'm in the process of writing my POH and Test Plan and can't seem to get a handle on at what RPM I can expect 55, 65 or 75% power. I realize this will only be confirmed after testing but I am looking for a starting point.

I have IO-360 power charts, but since I cannot adjust MP with the Prop control, where do I start?

I have a TMX IO-360 with a Sensenich 85 FP prop (the Van's recomended 360Prop).

I'm thinking I will see 65% at about 2400 RPM, can anyone flying a RV-7 with this combination share some numbers of what they actually see? (Any one altitude, I can adjust).

Sorry if this is a dumb question or if it's in the wrong forum.... Thanks

Larry

 

[hevansrv7a]

It depends

You will need a MAP instrument to approximate PctPwr. RPM alone is not a good indicator. For example, 2700 rpm at 9000 feet DAlt if you can even do it, will be 75% more or less. But if you can do 2700 at sea level DAlt you will be at approximately 100%. These example numbers are approximate for many reasons and merely illustrate the problem. You can search this forum extensively for formulae on PctPwr once you have the necessary data. In addition to MAP I think you will want an OAT and of course, a sensitive altimeter. You will also want to know the accuracy of your instruments.

 

[tomwebster]

I have an O-360/Sensenich-85 prop
I had a simular problem trying to maintain
75% power to break-in my engine. I started
without wheel fairings and finished with everything
installed. I also looked for a power chart I could
use easily in the cockpit. I have not found one.

An inaccurate but usable formula is to take the
sum of hundreds of rpms and add the manifold
pressure to equal 48 for ~75% power.

IE: 2400 rpm & 24" MP = 48 ( ~75% power )
2500 rpm & 23" MP = 48 ( ~75% power )
2650 & 21.5" = 48 = ~75%

The above formula is quite inaccurate, but works fine
for keeping the power in the 75% ball park for breakin.

Tom

 

[n5lp]

Kevin's Spreadsheet

Kevin Horton has developed spreadsheets that make a good estimate of power percentage. You input temperature, altitude, MP and RPM and it spits it out.
http://go.phpwebhosting.com/~khorton/rv8/

Go down the left side of the page to "Top Links."

Since it is inconvenient to use a PC in flight, I used Kevin's spreadsheet to make a little cheat card that I keep by my arm. It is slightly less accurate than the spreadsheet but much better than the "rule-of-thumb" methods.

To give you an idea what I have (different engine) here is my card. http://n5lp.net/Power.htm

 

[pierre smith]

Simple?

How's this? Pretty simple, pretty close for my 0-360 Catto powered -6A. It just ain't that critical,

Right next to the throttle,..alt, revs, %

Regards,

 

[lrfrey]

Thanks to all of you. I'm comfortable now with my approximations such that I can prepare my test plan. I have MAP, OAT, Altimiter etc so after the first flight I should have a pretty fair handle on actuality.

As Tom, I just want to keep the power up for breakin and yet not cook the sucker

Thanks again, Larry